Scratch storage

1. Currently climix leaves behind the dask scratch directory dask-worker-space in the calling directory. This should be removed upon exit, at least when finishing successfully.
2. When running climix on a NSC compute node, which would be the normal use case (for now), there is local disk scratch space available. This is available via the environment variable $SNIC_TMP and should provide fast disk i/o independent of /nobackup (nfs) load level. Moreover, it has the advantage that it is automatically cleared when the job/session is done.